Dry-running compressors are generally piston-type machine in which the gas-compression chamber must be kept free from particles of the liquid lubricants normally used upon the other parts of the machine to prevent wear or to provide an effective seal. A typical application for such dry-running compressors is the compression of oxygen in which the presence of liquid components, especially oil, is highly disadvantageous and unsafe for most uses.
For an effective separation of the lubricant-coated parts from the compression chamber of such dry-running compressor, it is customary to provide oil-stripping rings or the like as part of the seals separating the lubricant-containing chambers from the chamber exposed to the gas to be compressed. Such oil-stripping rings can remove the oil film mechanically from the piston rod, for example, and prevent practically any incursion of the oil into the space to be later occupied by the gas or traversed by those piston parts which come into contact with the gas.
It is therefore important that the gases processed in a dry-running compressor be free from liquids and especially from the lubricating oil of the dry-running compressor. On the other hand, the presence of oils or, in general terms, liquid in the gas is indicative of a failure of the oil-stripping system and the sealing devices which prevent incursion of the oil into the gas spaces. In the past the techniques for preventing oil from bypassing the stripping ring and entering the gas space has been to periodically disassemble the apparatus and replace the parts when signs or air were noted, or to await the development of noticeable amounts of oil in the gas, using this as a sign that replacement of the oil-stripping rings and seals was necessary.
The disadvantages of such systems will be apparent since, in the first case, the apparatus was forced into a maintenance program unnecessarily prematurely in some cases while, with the other system, contamination of the gases and of the dry-running parts was necessary before corrective action could be taken.
It has been desirable to provide a substantially automatic system for the detection of liquid components in the gases of a dry-running machine of the aforedescribed type to permit operation thereof under optimum conditions.